High-tension fuse assembly and heater therefor



July 11, 1944. T. F. JOHNSON HIGH TENSION FUSE ASSEMBLY AND HEATER THEREFOR Filed Sept. 24, 1942 within the tube.

Patented July 11, 1944 UNITED STATES PATENT OFFICE HiGnJrENsIoN FUSE ASSEMBLY AND HEATER THEREFOR y 3 Claims.

rIhis invention relates to high tension fuses of .the type used on transmission systems to cut off the current due to overloads or abnormal currents and, among other objects, aims to provide a relatively simple and effective heater associated with the fuse assembly to keep the fuse .lead wire and fuse element dry and thereby preM vent undue corrosion induced by corona efect The main idea is to provide a very cheap and effective heater element employn .ing eddy currents or induced currents within the -heater so arranged that it will produce sui- :iicient heat to keep the atmosphere within the tube relatively dry since it has been found that corona around the fuse lead promotes deterioration very much more rapidly when the humidity is relatively high within the tube.

Other aims and advantages of the invention will appear in the specification, when considered in connection with the accompanying drawing, wherein:

Fig. lis a longitudinal sectional View of a fuse tube assembly embodying one form of the invention;

Fig. 2 is a cross sectional View taken on the line 2--2 of Fig. 1;

Fig. 3 is a longitudinal sectional view of a portion of a fuse tube showing a modied heater;

Fig. 4 is a longitudinal sectional view of a portion of the fuse tube showing a further modiiied heater; and

F'ig. 5 is a sectional view similar to Figs. 3 and 4 but showing still another modied form of heater.

Referring 'particularly to the drawing, the type of fuse assembly selected for illustrative purposes is generally Similar to that shown in my Patent No. 2,230,955 issued February 4, 1941, which discloses such a fuse employed in a drop-out fuse assembly; although it may be like that shown in my Patent No. 2,269,372 issued January 6, 1942, or any other type. Furthermore, such fuses may be of the stationary type in which the fuse leads are ejected from the tube. In such fuse assemblies, it has been found that corona eats the fuse leads and ultimately destroys them, the rate of destruction being roughly proportional to the moisture content of the air around the leads and to the voltage. In accordance with this invention, the eddy currents around the fuse lead are employed to produce suicient heat to keep the air relatively dry within the fuse tube.

Referring now to the drawing, for a clear understanding of the invention, it is sufficient t state that the fuse assembly comprises an insulating tube I0 carrying upper and lower contact members II and I2 respectively, the lower contact member being articulated so that the fuse assembly can drop out as disclosed in my aforesaid Patent No. 2,230,955. The upper contact member is provided With a fuse receiving opening I3 through which is threaded the usual fuse element having a button member I4 and a fusible section l5 to which is connected a flexible lead IG extending downwardly through the tube and electricallyv connected to the lower contact element I2. When the fuse blows, due to overload, it will be understood that the fuse lead is ejected from the tube through the lower end. As shown, the fuse lead is spaced from the inner wall Il of the fuse tube, although this is not essential.

In Figs. l and 2, there is shown a heater element in the form of a metal sleeve or tube I8 composed of magnetic material, preferabiy iron, and insulated from the fuse lead by an insulating coating or covering I9 applied on the fuse lead I6, the arrangement being such that the eddy currents around the fuse lead will cause induced current to ow around or in the heating tube and heat it by resistance sufficiently to keep the lead I6 dry. This heater I6 maintains a higher temperature within the tube ii) than the atmospheric temperature on the outside. It has been found that a relatively thin sleeve or tube of iron only a few inches long and arranged in the lower portion of the fuse tube will serve the purpose, maintaining the temperature above, say, one hundred degrees within the tube. It will be understood by those skilled in the art that the amount of heat generated in the iron tube will depend upon the current ilowing in the fuse lead, the length of the iron tube, its cross sectional area and the composition of the iron or resistance offered by the iron or other metal oi which it is made.

Actual demonstrations have shown that a heater applied to a fuse assembly in this manner has greatly prolonged the life of iuse leads by practically eliminating the destructive effect of corona. In fact, the heater reduces the destructive effect to a point where it is no longer a source of trouble. Thus, it reduces the cost of maintenance and relieves linemen of the necessity of making very frequent inspections and replacing the vital fuse parts which are relatively expensive. Even in the enclosed type of fuse lead, considerable moisture trouble is experienced due to sweating of the fuse lead, which is obviated by the heater.

It is also within the scope of this invention to provide aS a heater, a resistance, in series with the fuse lead, as shown in Fig. 5. For this heater the current passing through the fuse lead 3U also passes through a short resistance wire section 3l which becomes slightly heated to thus heat the inside of the fuse tube 2%] and the lead wire. The resistance wire is preferably round in cross section and is brazed or otherwise secured in series with the flexible lead wire. This particular type of heater is especially useful in fuse assemblies carrying small currents.

Fig. 3 shows a further modified heater in the form of a cylindrical metal tube section 2| against the inside Wall of the fuse tube 2D, which is held in place in a counterbored portion 22 of the tube 2i! by means of a set screw 23. This tube 2l, as well as the sleeve f8, may be made of iron or steel, as well as any one of a number of highresistance alloys which are well knownv in the art. As an example of the size of a heater tube, the heater 2| may be two and one-half inches long and one-sixteenth of an inch thick.

The form of heater shown in Fig. 4 is of the transformer type having an iron tube 2# in the oounterbored portion 25 of the fuse tube 2S. A cylindrical layer 26 of insulation separates the tube 26 from a short-circuited coil 2l. A sleeve 28 retains the tube 24 in place and this sleeve is held in place by a screw 29.

If the heater is in the form of a short-circuited coil of high-resistance wire, it can be effective with twenty-five turns, for instance, assuming that two and one-half amperes of current are flowing in the fuse lead. This will raise the temperature of the fuse lead 30, which is more thanis required to produce the desired results. As a matter of fact, a few degrees above surrounding air temperature is all that is necessary.

Obviously, the invention is not limited to the particular forms thereof herein shown and described, but is capable of embodiment in various combinations and subcombinations.

I claim:

l. In a high tension, expulsion fuse assembly of the character described, wherein a fusible link is located near the upper end of an insulating tube and along, flexible lead Wire, constituting the current conductor, is connected to the fusible element and extends through the lower end of the tube so that it is exposed to the corrosive action of corona and moist air within the tube, an electric heater element associated with said lead Wire at a distance from the fuse link utilizing current derived from the lead Wire to heat it slightly within the confines of the tube and serving the sole purpose of preventing water of condensation from collecting on and corroding the lead wire, without influencing the rupture of the fusible link due to an over-load.

2. In a high tension, expulsion fuse assembly, as set forth in claim l, wherein the electric heater element is of the induction type and is located within the tube.

3. In a high tension fuse assembly comprising an insulating tube carrying a fusible element and a flexible lead Wire connected thereto and projecting through one end of the tube, an induction heater of the transformer type within the fuse tube around the lead wire and remote from the fusible element to heat the lead wire to a temperature slightly aboV-e that of the atmosphere and thereby prevent Water of condensation from collecting thereon.

.TOMLINSON F. JOHNSON. 

